Respiratory tract infections (RTIs), defined as any infection of the respiratory tract, are a leading cause of non-institutionalized illness and result in burden on the healthcare system and associated costs. Upper respiratory infections (URIs) are RTIs that affect the upper airway. URIs are the most common type of RTI and are predominantly viral with less than 15% attributable to bacteria. The estimated incidence of viral URIs in adults residing in the United States (U.S.) is approximately 2.5 episodes per person annually, which burdens the healthcare system and negatively impacts productivity at work and school.
The term “common cold” is often used interchangeably with URIs by the general public; however, the medical community defines the common cold as a clinical illness wherein expression of symptoms results from a viral-induced URI (Barrett et al., 2009). In terms of a medical diagnosis, the ICD9 code terminology classifies acute nasopharyngitis/common cold as code 460. Psychological stress and poor mental health (e.g., depression, anxiety, and exhaustion) has been associated with higher risk for acquiring URIs. Typical symptoms of URIs include sneezing, nasal discharge or obstruction, sore or scratchy throat, hoarseness, and cough; headache, myalgia, malaise and fever may also be present. Symptom severity typically peaks 2-3 days after infection, with a mean duration of approximately one week with 25% of cases lasting longer. URIs can exacerbate pre-existing conditions such as asthma, or can lead to other illnesses such as otitis media, sinusitis, or a lower RTI (i.e. bronchitis, bronchiolitis, tracheitis and pneumonia).
Despite the viral etiology of most URIs, antibiotics are commonly prescribed to treat symptoms, a practice that contributes to antibiotic drug resistant bacterial strains. There is no evidence that over-the-counter (OTC) drugs have any effect on the duration of the viral infection, and they offer only marginal benefits with regard to alleviation of symptoms. Further, OTC drugs may have unwanted side effects, such as drowsiness, xerostomia (dry mouth), nervousness, irritability, difficulty sleeping, and elevated blood-pressure. More serious consequences with OTC drugs are also possible. For example: liver toxicity due to co-ingestion of acetaminophen and alcohol, and gastrointestinal bleeding or renal toxicity in response to aspirin and non-steroidal anti-inflammatory agents.
Characteristics of URI symptoms (for example, duration and severity), and functional impairment in response to symptoms, impact health-related quality of life (HRQL) during URIs (Barrett et al., 2009). Various aspects of HRQL can be negatively affected during URIs, such as: physical functioning, bodily pain, vitality, social functioning and mental health. Thus, there is interest in strategies that can improve HRQL in persons suffering from URIs.
The administration of probiotics, defined by the World Health Organization as “live organisms which when administered in adequate amounts confer a benefit on the host” is a safe nutrition intervention in the generally healthy population. Probiotics are found in the human intestinal tract and commonly present in yogurt and other food items (e.g., beverages, cereals and chocolate candy bars).
Probiotics have been investigated for their ability to modulate immune function, and positively impact clinical outcomes related to atopic allergies, respiratory allergies, RTIs, gastrointestinal diseases, periodontal infections, and female urogenital conditions. Oral supplementation of certain probiotic strains has demonstrated immunomodulatory effects in healthy adults.
Probiotic strains may help prevent and treat RTIs in children and adults. However, there are some limitations to the prior art findings. For example: sample sizes were too small to detect differences between groups with regard to incidence rates; some studies did not differentiate URIs from lower RTIs; results were confounded by the use of prebiotics; and severity has only been assessed in two studies of normal healthy adults (Bergren et al., 2011; and de Vrese et al., 2005).
The only published study on a composition of Lactobacillus rhamnosus GG and Bifidobacterium animalis subsp. lactis for use in the treatment of respiratory infections relate to infants (Rautava et al., 2009, and WO2006007526). The study by Rautava et al., 2009, was a randomized, double-blind, placebo-controlled trial in 81 infants using an infant formula containing Bifidobacterium lactis Bb-12 and Lactobacillus rhamnosus GG for up to 12 months and a formula without probiotics as a control. Incidence of recurrent (≧3) RTIs was lower in response to probiotics versus placebo (P=0.031). Rautava et al., 2009, found that the incidence of acute otitis media as a consequence of URIs was lower in response to probiotics versus placebo (P=0.027). The duration or severity was not registered.
The study did not report on severity of RTIs. Further, the study is not generalizable to an adult population due to inherent differences between the immune systems of children, in particular infants, and adults.
A number of published studies have investigated the efficacy of probiotics in reducing the incidence, duration and severity of URIs in adults. These studies provide evidence that certain probiotic strains may be effective in reducing the duration and severity of URIs and RTIs in generally healthy adults, when compared to non-probiotic controls. None of these studies were made with a composition comprising the combination of Lactobacillus rhamnosus GG and Bifidobacterium animalis subsp. lactis. 
Mixed results in the published probiotic studies underscore the notion that not all probiotics are created equal, and the beneficial effects of probiotics on URI outcomes appear to be strain specific and may work optimally in combination.